Escapement pawl control



Jan. 7, 1958 T. H. TOEPPEN ET L ESCAPEMEINT PAWL CONTROL 2 Sheets-Sheet 1 Filed Dec. 29, 1955 IN VEN TORS THURSTON HIOEPPEN By ROBERT .DONNNN fiv ATTORNEY Jan. 7, 1958 T. H. TOEPPEN ET AL ESCAPEMENT PAWL CONTROL Filed Dec. 29, 1955 2 Sheets-Sheet 2 ESCAPEMENT PAW L CONTROL Thurston H. Toeppen, Hyde Park, and Robert A. Donnan, New Paltz, N. Y., assignors to International Business Machines Corporation, New York, N. Y., a corporation of New York Application December 29, 1955, Serial No. 556,153

8 Claims. (Cl. 197--85) This invention relates to typewriters, and more particularly to an improved pawl control mechanism for the escapement action of a typewriter carriage.

In conventional typewriter escapement actions, the escapement pawl is pivotally mounted for rocking and longitudinal movement through the interaction of an elongated slot and pivot pin. With this conventional construction, when a pawl is tripped, it travels by spring action toward the next escapement rack tooth within the limits of its elongated slot, and then the escapement rack drives the pawl longitudinally so that the opposite end of the slot engages the support pin thereby terminating one escapement action.

Admittedly, this conventional mechanism works satisfactorily for normal escapement, but it does create problems in both back space and carriage return operations since in both these actions, the carriage must be moved through a distance measured by tooth pitch plus twice the slot clearance, thereby necessitating an over bank travel when carriage is returned to left hand margin, and a long throw for a back space pawl.

It is a first object of this invention therefore, to provide an improved no travel escapement pawl mechanism.

It is a further object of this invention to provide an improved no travel escapement pawl wherein a back space operation can take place without having to move the carriage the pitch distance plus the over travel in order to accomplish one backspace operation.

It is a still further object of this invention to provide a no travel escapement pawl wherein the overbank required for carriage return can materially be reduced.

It is a still further object of this invention to provide an improved pawl control mechanism, as a result of which the tabulation action can take place in shorter time.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

\ In the drawings:

Fig. 1 is a perspective view of a typewriter escapement control mechanism.

Figs. 2a through 2d are plan views showing the relation of the escapement mechanismwith a carriage rack during an escapement operation.

Fig. 3 is a plan view of both an escapement and backspace mechanism with a carriage rack.

.Briefly, this invention relates to an improved escapement pawl mechanism wherein a holding pawl which has pivotal but not longitudinal movement is used in conjunction with an interposer and latch control pawl to effect an escapement action.

With reference to the drawings, and particularly to Fig. 1, a type bar 2 of a well known IBM type bar drive mechanism, is shown pivotally mounted about a fulcrum 4 for movement under control of a cam lever 6 which is rocked about its own pivot 8 in response to the interengagement States atent of a cam 10 and power roller 12. The cam 10, in turn, is rocked into engagement with the power roller via a key lever 14 actuating a trip latch 16.

As the type bar is driven towards print position, it engages a U-bar 18 which is resiliently supported by a leaf spring 20 to permit limited transverse movement. The U-bar 18 is equipped with a link 22, and during a print stroke, the transverse movement of the U-bar acting through link 22 rocks a trip lever 24 which is pivotally supported by a pin 26 for movement into and out of engagement with the escapement pawl mechanism 28.

A carriage escapement rack 30 is biased by the usual spring motor (not shown) in the direction of the arrow. Consequently, each time the pawl mechanism is released from the rack, the carriage advances under action of its spring motor relative to the pawl mechanism.

Pawl mechanism The essence of this invention lies in the cooperation of the trip lever 24 in conjunction with the new and improved pawl system 28. Pawl mechanism 28 (Figs. 2a-2d) comprises an interposer 32, a latch pawl 34 and a holding pawl 36, all superimposed and pivotally supported about a stud or pin 38 which is secured to the typewriter frame. Each of the members of the pawl system is equipped with an ear 40, 42, 44 respectively engageable with a. corresponding spring 46, 48, 50 respectively to provide the necessary ro tational or translating force to the respective members.

Since the rack is always to be held by the holding pawl 36, provision is made for pivoting the latter about pin 38 without permitting translation relative to it. The latch pawl 34, and the interposer 32, however, are slotted to permit both pivotal movement as well as translation relative to pin 3% Furthermore, the interposer 32 has a trip ear or shoulder 33 engageable with the trip lever 24. .In the normal or rest positions of Fig. 2a, the trip ear 33 will act on the tails of both the latch pawl 34 and the holding pawl 36 to pivot them. With additional reference to Fig; 2a, the latch pawl 34 (upper one) is slotted at its pivot point so that the distance from the right hand end of its pivot slot to its rack tooth holding surface (or nose) is less than that of the holding pawl 36 thereby, assuring the fact that in rest position (Fig. 2a), the holding pawl is the only one blocking movement of the rack 30. Thenose of the latch pawl 34 is slightly shorter than that of the holding pawl 36, therefore, when the two pawls are pivoted about pin 38, the latch pawl nose is free of the rack 30 slightly before holding pawl nose and, therefore, can be tripped, i. e. pulled to the right by its spring 48.

With this understanding of the pawl mechanism 28, the best way of describing the operation of this invention is to explain what takes place as a type bar moves into printing position (e. g. pawl movement from Fig. 2a to Fig. 2d position).

Fig. 2a shows the rest position of the parts with the nose of latch pawl 34 and hold pawl 36 engaging rack tooth 52, and then in Fig. 2b, the trip lever 24 has moved forward to rock the interposer 32 which, in turn, pivots the latch pawl 34, and the hold pawl 36, to the point where the latch pawl is tripped and slides over the tooth 52 under the action of its spring 48, but the holding pawl 36 is still not quite out of engagement of the tooth 52. Note that in the Fig. 2b position, the tail of the latch pawl 34. is free of the interposer trip ear 33. p

In Fig. 2c, the escapement trip lever 24 has moved forward still further to lift the holding pawl out of the rack, and in the meantime, the latch pawl has engaged the next tooth 54. With the holding pawl disengaged, the rack is driven to the left toward Fig. 2d position under the action of the carriage spring motor. During this movement, the tail of the latch pawl 34 engages the side .ofzear;

3 33 thereby driving interposer 32 to the left to a point where the tail of holding pawl 36 unlatched, i. e. free of ear 33, whereupon spring 50 drives holding pawl 36 back into the rack to engage tooth 54 and stop the rack.

Incidentally, the relative positions of the escapement trip lever 24 with respect to the latch pawl 34 is such that the two can never be in engagement, and consequently, it is impossible for the rack to be held by the tail of latching pawl 34 being wedged against the side of the trip lever 24 when the latter has been moved to a tripping position. Nor will the latch pawl hold the rack if a type bar is held in printing position, since the latch pawl, as previously described will unlatch the holding pawl from the trip ear 33 of the interposer 32.

With the understanding that all rack holding is done only by the holding pawl, it can be recognized that there is no need for over travel in movement of the rack in either direction. For example, during a backspace operat'ion (Fig. 3) when a backspace mechanism 54 is actuated, as later described via a pull on a link 56, back space pawl 60 is driven about its pivot stud 58 into the rack causing the rack to be moved in the direction of the arrow of Fig. 3. Fig. 3 shows the termination of a backspace movement wherein backspace pawl 60 has been moved the clearance distance between slot 59 and stud 58. The rack need only be moved far enough to permit the holding pawl 36 to slip over the next succeeding rack tooth (e. g. from 54 back to 52). Actually, there is a slight safety factor of movement to provide clearance (but if a conventional pawl were employed, the rack would have to be moved an additional distance equal to the displacement between the noses of pawls 34 and 36 as viewed in Fig. 3). From the Fig. 3 position, after the pull on link 56 has been relaxed, the rack is driven into engagement with the holding pawl again (while latch pawl 34 retains its Fig. 3 position), pressure will be taken off backspace pawl 60 whereupon springs 62, 63 will restore the backspace mechanism to its rest position.

On the next type bar print stroke, the ear 33 of interposer 32 will engage only the tail of holding pawl 36, since the latch pawl is already in its Fig. 2b position.

The backspace mechanism, as is well understood in the art, is under control of a key lever 64 which is connected via a link 66 to a trip lever 68 of a backspace cam mechanism 70. The latter is pivotally supported about a fulcrum 72 for engagement of a cam 74 with the power roll 12. When the key lever 64 is depressed, the cam is rocked into engagement with the power roll to be driven through a half revolution whereupon the cam holder 70 is rocked to pull on link 76 and then via bell crank 78 to pull on link 56, for the backspace action heretofore described.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. In a typewriter having a carriage including a carriage rack spring biased in character spacing direction, an improved pawl control for the escapement action of the carriage comprising an interposer, means pivotally mounting the same for movement into and out of a tripping position, said interposer being further provided with means permitting transverse movement relative to said pivotal mounting means, a holding pawl mounted for pivotal movement only with respect to said mounting means from a rest position wherein it is biased into en gagement with said rack to a release position, means interconnecting said interposer and said holding pawl to lift said holding pawl out of said rack in response to said interposer being moved to tripping position, and means responsive to carriage movement during an escapement action for disengaging said interposer from said holding pawl to permit the latter to re-engage said carriage rack.

2. In a typewriter having a carriage including a rack spring biased in character spacing direction, an improved pawl assembly for regulating the spacing of said carriage comprising a holding pawl, an unlatching pawl, and an interposer all mounted for tripping movement during an escapement action with said pawls being movable from a rest position wherein they are biased into engagement with said carriage rack through a tripping range to a rack release position, said unlatching pawl and said interposer being further provided with means permitting transverse movement relative to said holding pawl, said interposer being still further provided with portions engageable with both pawls to trip the same during an escapement action, said unlatching pawl when tripped having means biasing the same in a direction opposite to carriage travel and free of said interposer portions so that said unlatching pawl may again be biased into engagement with said carriage rack whereupon, as said carriage moves during an escapement action, said unlatching pawl is driven into engagement with said interposer to unlatch said portion-s from said holding pawl permitting the same to drop back into engagement with said carriage rack.

3. In a typewriter having a carriage including a rack biased in character spacing direction, an improved escapement action having an escapement pawl cluster comprising a holding pawl, an unlatching pawl, and an interposer with all of said parts being mounted for tripping movement from a rest position wherein said pawls are biased into said carriage rack to a trip position wherein said pawls are disengaged from said rack thereby releasing the latter for movement, said interposer having portions engageable with said pawls to trip the same when said pawl cluster is in grouped position, said interposer being biased into cluster grouped position while said unlatching pawl is biased normally out of grouped position but is driven into cluster grouped position by said carriage during an escapement operation, said unlatching pawl in being driven back into cluster grouped position being engageable with said interposer when the latter is in its tripping range to drive the same out of grouped position thereby permitting said holding pawl to re-engage said rack.

4. In a typewriter having a carriage including a rack biased in character spacing direction, an improved escapement action having a pawl cluster comprising a holding pawl, an unlatching pawl, and an interposer, means mounting said holding pawl for pivotal movement only while said unlatching pawl and said interposer are mounted for both pivotal and transverse movement, said interposer having portions engageable with said pawls when said cluster is in grouped position to trip the same from a rest position wherein said pawls are biased into said rack to a trip position wherein said pawls are disengaged from said rack thereby releasing the latter for movement, said interposer being biased normally into cluster grouped position while said unlatching pawl is biased normally out of cluster grouped position but driven into cluster grouped position by said carriage during escapement, said unlatching pawl in being driven to grouped position being engageable with said interposer when the latter is in its tripping range to drive the same out of groupingposition thereby permitting said holding pawl to re-engage said rack.

5. In atypewriter having a carriage biased in character spacing direction, an improved pawl control for the escapement action of the carriage comprising a holding pawl, means mounting the same for pivotal movement only and including means biasing the same into engagement with said carriage, an interposer operable during each escapement action to trip said holding pawl free of said carriage, and an unlatching pawl engageable with said interposer during an escapernent action, said unlatching pawl being biased into engagement with said carriage and having provision for biased longitudinal movement relative to said mounting means to be free of said interposer after being tripped until said carriage advances in letter spacing operation whereupon said unlatching pawl will strike said interposer if the latter is in its tripping range to disengage the same from said holding pawl to permit the latter to drop back into carriage engagement.

6. In a typewriter having a carriage biased in character spacing direction, an improved pawl arrangement for the escapernent action of the carriage comprising a sup porting stud, an interposer pivotally mounted for movement from a rest position into a tripping position about said supporting stud during an escapement action, said interposer being further provided with means to permit transverse movement with respect to the direction of said tripping action, spring means biasing said interposer normally in one direction of said transverse motion, and a holding pawl mounted on said supporting stud for pivotal movement from a rest position wherein it is biased into engagement with said carriage to a tripping position wherein said carriage is free for movement, said holding pawl being engageable with said interposer only when the latter is biased in its normal direction whereby during an escapement action as said interposer is driven into tripping position, said holding pawl is lifted out of said carriage to release the same for escapement.

7. A mechanism in accordance with claim 6 being further provided with means responsive to carriage move ment during an escapement action for disengaging said interposer from said holding pawl thereby permitting the latter to drop back into the carriage.

S. A mechanism in accordance with claim 6 being further equipped with an unlatching pawl which is pivotally supported about said mounting stud for transverse movement and pivotal movement from a carriage engaging position to a trip position in response to said interposer being moved to tripping position, said unlatching pawl when in its trip position being spring biased out of engagement with said interposer whereupon said carriage rack drives said unlatching pawl into said interposer thereby unlatching said interposer from said holding pawl permitting the latter to drop into the carriage.

Thompson el al. Mar. 19, 1935 Yaeger Jan. 2, 1951 

